Tolerance is used to specify by how much a dimension can vary. Geometric tolerancing is a way to show maximum allowable deviations of form, profile, orientation, location, and run-out of a feature.
The first of two mandatory symbol frames contains a symbol that represents the geometric characteristic to which a tolerance is being applied, such as form, orientation, or run-out. Form tolerances control straightness, flatness, circularity, cylindricity, and profiles of lines and surfaces. The second mandatory frame contains the tolerance value. Where applicable, the tolerance value is preceded by a diameter symbol and followed by a material condition symbol. For a tolerance frame with two tolerance values, the second compartments contains the value of Tolerance 1 and is followed by a third, identical compartment that holds the value of Tolerance 2. Other (optional) compartments commonly contain a pair of symbols each. These are a datum reference letter and a material condition symbol.
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